The .44 Remington Magnum, also known as .44 Magnum or 10.9x33mmR, is a rimmed, large-bore cartridge originally designed for revolvers and quickly adopted for carbines and rifles. Despite the ".44" designation, guns chambered for the .44 Magnum round, its parent case, the .44 Special, and its parent case, the .44 Russian all use 0.429 in (10.9 mm) diameter bullets. The .44 Magnum is based on the .44 Special case but lengthened and loaded to higher pressures for greater velocity and energy.

A rim is an external flange that is machined, cast, molded, stamped, or pressed around the bottom of a firearms cartridge. Thus, rimmed cartridges are sometimes called "flanged" cartridges. Almost all cartridges feature an extractor or headspacing rim, in spite of the fact that some cartridges are known as "rimless cartridges". The rim may serve a number of purposes, including providing a lip for the extractor to engage, and sometimes serving to headspace the cartridge.